BASILICA, a word frequently used in Latin literature to designate a large, roofed building dedicated to public use. Mar kets, court-houses, covered promenades and meeting halls are all occasionally so known. Little by little the word was limited to buildings of a more or less definite form, having a central area, aisles or galleries at the sides and a raised platform, sometimes apsidal. These elements, nevertheless, are not constant, the Basil ica Julia in Rome having no apse, and that at Timgad no aisles. The basilica was usually in a forum (Basilica Julia, Trajan's basilica, the basilica at Pompeii). For what a Roman architect considered a normal basilica one may consult Vitruvius v. 1.4 and vi. 3.9.
The earliest basilica known is that at Pompeii, which dates, probably, from the 2nd century B.C. It shows an already highly developed form in which the aisle runs entirely around the central area with the raised platform appearing as an alcove, screened by columns, at the end opposite the entrance. This seems the normal plan for the larger basilicas. The basilica of Maxentius or Constantine, begun by Maxentius and completed by his suc cessor, Constantine, is, however, of an entirely different type. Here the attempt was made to dispense with the colonnades and to concentrate the supports into a few enormous piers, which carry the three bays of the groined vault over the central area and at the same time furnish the dividing line between the bays of the lower side aisles. It was the application to the basilica problem of the type of construction and decoration developed in the great halls of the Roman baths.
Besides these large basilicas there were many smaller examples, and in some of these, as in the basilica of the palace of Domitian on the Palatine hill, the type comprising a nave with aisles at the sides only and an apse at the end had appeared. It was this type that the early Christians adopted for their churches, possibly because similar halls, in large private houses, had been used for Christian worship prior to the Edict of Toleration. It would ap pear that, in the earliest examples, side aisles were frequently lacking. After the time of Constantine, however, the existence of side aisles is universal, and is perhaps due to the fact that they were included in the three enormous basilicas—those of St. Peter, St. Paul and St. John Lateran—which he built. The church of St. Maria Maggiore, dating in its present form from the early 5th century, is similar to its three predecessors. In the Constantinian basilicas another unit, the transept (q.v.), made its appearance, and the cross-shaped plan thus developed became the controlling plan of the larger Christian churches in the West throughout the middle ages.
In the typical early Christian basilica the nave (q.v.) was sep arated from the side aisles by borders of columns which carried either arches or an entablature. In the later basilicas these col umns, having been taken from older pagan buildings, frequently had misfit capitals. Above the entablature or arches rose the blank wall behind which were the side aisle roofs; this wall con tinued up as a clerestory and was pierced with a row of either square or arched windows. The nave roof was of timber, some times with exposed beams and sometimes with a rich, panelled wooden ceiling, carved and gilded. Side aisles (see AISLE) were either single or double, and occasionally of two storeys, the upper serving as a gallery for women. The side aisle ceilings, with the roof immediately above, were usually as low as the columns would permit; but in old St. Peter's, Rome, the inner aisles were much higher than the outer, which were vaulted. The apse (q.v.) opened from the nave by a great arch known as the triumphal arch. Occasionally, when there were transepts, another triumphal arch separated the transept from the nave. A narthex (q.v.), or vestibule, extended the entire width of nave aiid aisles, frequently open at the front with a colonnade. In addition to these general elements, there was frequently a transept, usually without aisles, at the extreme end. At the entrance end, in addition to the narthex, there was often a court or atrium (q.v.), surrounded by either colonnades or arcades. After the loth century a campanile (q.v.), round or square, of great simplicity and usually very high, was added.
Such a building was basically simple ; the exterior design was crude to the point of being barn-like, although there were occa sional exceptions : old St. Peter's at Rome had a facade richly cov ered with mosaic, and San Lorenzo Fuori, Rome, has a handsome colonnade across the front. After the fall of Rome the interiors likewise show architectural poverty, all sorts of pagan Roman fragments being put together in meaningless and incoherent jum bles. All, however, possess interior interest and an inherent beauty due largely to the richness of their furniture and ornamentation. The decorative scheme shows that the feeling for colour and tex ture increased as the purely architectural sense decayed, and the development of a technique of glass mosaic offered great oppor tunities for impressive effects. The lower portions of the walls were usually sheathed in coloured marbles which were frequently of rich design around the apse. Above the arches or entablatures of its flanking columns the nave wall was sometimes completely covered with mosaic; where this is absent, painting of similar character doubtless existed. The church of Sta. Maria Antigua, at the base of the Palatine hill, shows many examples of such painting.
The climax of the decorative scheme was the triumphal arch and the mosaic of the dome of the apse. There is no formula for these decorations. They vary from the Byzantinesque figures of Sta. Maria in Trastevere to the rich spirals of the vine of San Clemente. They are always full of complete symbolism (see Strzygowski's The Origin of Christian Art) . The furniture con sisted of a choir screen with one or two ambones (see AMBO), the clergy seats and the bishop's throne in the apse, and the altar, with a baldachino (q.v.) or canopy above it. All this furniture was as lavishly ornamented as possible. Its framework was usu ally of white marble, in which were inserted plaques and roundels of dark marble and bands of mosaic, sold, red and green. Fre quently the floor was also rich with marble and mosaic (q.v.) of this type, known as opus Alexandrinum.
Although the basilica is primarily characteristic of Rome, there are many examples elsewhere. In addition to the one at Parenzo, the basilica of S. Apollinare Nuovo, erected by Theodoric at the beginning of the 6th century and that of S. Apollinare in Classe 5o years later, both at Ravenna, are particularly noteworthy. In the east, the great church of St. Simeon Stylites in Syria is of modified basilica type. The church of the Nativity at Bethlehem is a basilica, as is also the church of St. John Studios in Con stantinople, but the finest example in the eastern empire was St. Demetrius at Thessalonica (Salonika). Owing, however, to the example set by Justinian's great church of S. Sophia at Con stantinople, the basilica form gradually passed out of use in the eastern church. Few remains exist of the earliest churches built in the north and west of Europe. England shows occasional fragmentary ruins, such as the foundation of the 4th century basilica at Silchester. Romanesque rebuilding everywhere except in Italy destroyed these early churches, yet the basilica type left an ineradicable stamp on all church building that succeeded and the basilica plan, with its nave, aisles and apse, became, with the development of vaulting, and the changes necessitated by it, the typical church building of the western church.